This invention relates to a manifold assembly for supplying and removing a fluid, upon command, to a plurality of solar energy collectors for heating and/or energy exchange by absorption. More specifically, the invention relates to a manifold assembly which interconnects a plurality of tubular solar energy collectors with each other, in parallel, to form a bank of collectors, and which further interconnects a plurality of banks of collectors with each other, in series to form a tiered arrangement, for the delivery of a heat exchangeable liquid under pressure in one direction, and for the return of the liquid under gravity in the opposite direction, upon command. The manifold assembly, in combination with other apparatus, provides a capability for a batch system operation and/or a continuous system operation. Additionally, the manifold system provides a capability for quickly filling tubular solar energy collectors with a heat exchangeable liquid under pump pressure and for quickly and completely draining the tubular solar energy collectors under gravity, to yield a fail safe operation regarding freezing conditions and/or boil-out conditions. Manifold systems used heretofore, primarily for tubular solar energy collectors, as contrasted to flat plate or panel collectors, have not been concerned with fail safe conditions, economics and simplicity. Rather, the heretofore mentioned manifold systems demonstrated feasibility for use with high performance tubular solar energy collectors. The circulating fluid, preferably water, remained in the manifold and collectors without provision for removal by draining. Thus the apparatus became vulnerable to damage by accidental freezing and boiling, caused by malfunction of the control system and the hydronic system. In addition, little consideration had been given to the loss of thermal energy when a large volume of water stagnated overnight inside the tubes, or to power consumption during continuous cycling of the fluid, or to servicing and maintenance of the system especially with hot water inside the collectors.
There are two basic types of solar energy collectors: (1) flat plate or panel collectors comprising a plate of glass and an energy absorbing surface therebelow and having a fluid circulating therein; and (2) tubular collectors comprising a double-walled configuration with a vacuum between the inner and the outer tube, and with the former having an energy absorbing coating on its outside surface and a fluid on its inside surface to absorb solar heat. The inherent differences between the two types dictate that what may be good for one type is not necessarily operable with the other. However, irrespective of the inherent differences, recent attempts with both types to rectify the above considerations have been met with other problems and/or tradeoffs. For instance, some attempts included the use of an anti-freeze solution to the heat transfer fluid, but the efficiency of the system was reduced due to the lower coefficient of heat transfer of the anti-freeze solution. With the flat plate collectors attempts have been made to batch operate and/or to provide a drainable system to safeguard against freezing and boil-out conditions. Generally, with flat-plate collectors, parallel tubing is employed to carry the fluid and drainability is feasible except that small diameter tubes are used to increase surface area and hence efficiency for heat transfer, and some fluid remains in the tubes due to surface tension. And, when larger diameter tubes are used, less efficiency is realized. Because flat plate collector panels have a low fluid capacity, a batch mode operation approaches a continuous mode operation due to the frequency of the "batching" and hence requires greater power consumption. Additionally, with flat plate collectors, should a malfunction develop or the fluid purposefully be drained during the day cycle, the collectors get very hot, causing damage to the tubing therein.
With the tubular collectors, early systems were capable of tiered arrangements, but operation was limited to a continuous mode, the apparatus was complex and the system was not drainable due in part to the serpentine configuration of the flow of the fluid within a bank or tier of tubular collectors. Recent attempts to provide a batch mode operation with tubular collectors have been met by other problems, including being unable to have a tiered arrangement thus limiting the capacity of the system, and drainability is so slow that power is required to drain the system of each "batch."
The present invention answers the above considerations and overcomes the problems by providing a batch mode operation in a real sense due in part to the large fluid capacity in the tubular collectors, a capability for filling a tiered arrangement of banks of the tubular collectors, a gravity-drain system, and by reducing power consumption.